Car Battery Problems: Slow Starts, Flat Batteries and Replacement

Early signs that a battery is tiring

The classic sign is a slow, labouring crank when you turn the key or press the start button, as if the engine is reluctant to wake up. Other clues are headlights that dim while cranking, a clicking noise instead of a start, interior electronics that reset themselves, or a battery warning light that flickers on the dashboard.

Do not dismiss a single slow start as a one-off. A battery loses capacity gradually, and the first hesitation on a cold morning is often the moment it starts running out of reserve.

• Slower or heavier cranking than usual, especially when cold.
• Dim lights or a dashboard that flickers during starting.
• Clicking sounds with no engine turnover.
• Radio presets, clock or trip computer resetting.
• Visible corrosion around the terminals or a swollen battery case.

Why cold weather and short journeys do the damage

A battery stores energy chemically, and that chemistry slows down in the cold. At the same time, a cold engine with thick oil needs more effort to turn over. So winter asks the most of a battery just when it can deliver the least. A battery that coped fine in summer may suddenly fail in November.

Short journeys add to the problem. Starting the engine takes a big draw of current, and the alternator needs some time at a reasonable speed to put that energy back. If most of your driving is a few minutes at a time through town, with lights, heated screen and heated seats on, the battery can end up slightly less charged after every trip. Over weeks that deficit builds up. A longer drive now and then helps, but it will not rescue a battery that is already worn.

Testing: is it the battery or the charging system?

A flat battery and a failing battery are not the same thing, and neither is the same as a charging fault. A battery may be flat because the lights were left on, because a component is drawing current while the car is parked, or because the alternator is not charging properly. Replacing the battery without finding out which applies can mean the new one goes flat too.

A proper battery test measures how well the battery holds charge and how much starting current it can deliver under load. A charging system check then looks at whether the alternator is putting out the right voltage with the engine running. If the battery keeps going flat after a good charge, electrical fault finding can look for something draining it overnight. It is a short list of checks, and it saves a lot of guesswork.

Stop-start and modern battery types

Cars with stop-start systems cut the engine at junctions and restart it, which means far more starts and a much heavier demand on the battery. They normally use an enhanced type of battery designed for that cycling, and many modern cars also have a battery management system that monitors the battery and adjusts charging.

This matters at replacement time. Fitting the wrong type can upset stop-start operation or shorten the new battery's life, and on some vehicles the replacement needs to be registered with the car's computer so charging is managed correctly. Ask what your car requires before assuming any battery that fits physically will do.

Replacement: what to expect

Batteries usually last a good number of years, but life varies with climate, driving pattern, vehicle demands and how well the charging system is working. There is no single date when every battery dies, so a test is more reliable than guessing from age alone.

If a replacement is needed, the main points to settle are the correct size and specification for your car, whether it needs coding or registration, and whether the old battery is disposed of properly. Cost depends on the type of battery and the vehicle, so ask for an estimate that explains what is being fitted and why. At Banks of the Tyne in Hebburn we can test the battery and charging system and replace the battery if it proves to be the problem.

Frequently asked questions